Start by generously seasoning your chuck roast with salt and black pepper. Place the seasoned roast into your crockpot. Arrange the diced potatoes, sliced carrots, and diced onion around the roast.
In a small bowl, whisk together the beef stock, Worcestershire sauce, minced garlic, garlic powder, onion powder, oregano, thyme, salt, and black pepper. Pour this mixture over the roast and vegetables in your crockpot.
Place the lid on your crockpot and set it to cook on low for about 7 to 8 hours or on high for about 6 to 7 hours.
Combine cornstarch with water in a small bowl to create a slurry. Pour this mixture into the crockpot while gently stirring until blended.
Add sliced mushrooms into the pot after thickening. Replace the lid and let them cook for an additional 10 to 15 minutes until they are tender.